The present invention relates to a method of closing the ends of tubular wrappings on a cigarette packing machine.
In particular, the present invention relates to a method of closing the ends of tubular wrappings on a continuously operating cigarette packing machine. In the following description, reference is made solely to closing the ends of inner wrappings of so-called xe2x80x9crigidxe2x80x9d packets of cigarettes, though, as will be clear to an average technician in this particular field, the same also applies equally to closing the ends of outer wrappings of so-called xe2x80x9csoftxe2x80x9d packs.
On continuously operating cigarette packing machines, groups of cigarettes are fed successively to respective conveying heads on a wrapping wheel unit, to which each group is supplied already partly wrapped in a respective sheet of wrapping material, normally foil, folded into a U about the group. As it is fed forward on the wrapping unit, each sheet of wrapping material is folded longitudinally at a folding station to form about the respective group a tubular wrapping having two end portions, each projecting from a respective end of the group, and each of which is later folded, at further folding stations, to close the end of the relative tubular wrapping.
On the wrapping unit wheels of known continuously operating packing machines, the tubular wrappings, as they are fed through the folding stations by the respective conveying heads, are normally maintained contacting the conveying heads by means of a cylindrical outer plate, which slides along, and so outwardly curves, an outer wall of each tubular wrapping. At relatively high production speeds, the fact that one of the walls on the tubular wrapping is curved may result, when closing the ends of the tubular wrapping, in improper folding of the end portions, thus resulting in the group being rejected.
U.S. Pat. No. 3,810,314 discloses a packing machine, wherein tubular wrappings are fed successively along a straight folding path and through two folding stations, in the first of which the short sides of a projecting tubular portion of each tubular wrapping are folded to define two projecting major tabs, and in the second of which the two major tabs are folded one towards the other. The straight folding path is defined by lateral fixed folding means and by upper and lower fixed supporting means, which contact the major walls of each tubular wrapping when such tubular wrapping is fed along the straight folding path.
However, the packing machine disclosed by U.S. Pat. No. 3,810,314 can be used only at relatively low production speeds, because when each tubular wrapping is fed along the straight folding path, the relevant major walls creep along the upper and lower fixed supporting means.
It is an object of the present invention to provide a method of closing the ends of tubular wrappings designed to eliminate the aforementioned drawback, and which is also straightforward and cheap to implement.
According to the present invention, there is provided a method of closing the ends of tubular wrappings enclosing respective groups of cigarettes.
In the method defined above, said two tabs are preferably folded as the relative said tubular wrapping is fed along a path parallel to said major walls; both said tabs being folded successively by means of a single rocker arm mounted to swing about a hinge axis crosswise to said path and comprising two arms located on opposite sides of said hinge axis and each having a respective folding edge for a respective said tab; said rocker arm being swung about said hinge axis so that each said folding edge interferes with said path in time with said tubular wrappings traveling along the path.
Using a rocker arm as described above in itself provides for solving another important problem encountered on most known continuously operating wrapping wheels, and which is the highly complicated mechanical design, and therefore relatively poor reliability and high manufacturing and maintenance cost, of such wheels. Known continuously operating wrapping wheels, in fact, normally feature an outer folding device common to all the conveying heads and for folding one of the major tabs of each end portion of each tubular wrapping, and a number of inner folding devices, each fitted to and movable with respect to a respective conveying head. As a result, the wrapping wheel must be fitted with mechanisms for controlling the inner folding devices, and which, being normally both complicated and bulky, further complicate the already complex structure of the wrapping wheels.
Using a rocker arm as described above, on the other hand, provides for eliminating all the inner folding devices, and for folding both the major tabs of each end portion of each tubular wrapping using one outer folding member.
The present invention also relates to a unit for closing the ends of tubular wrappings.
According to the present invention, there is provided a unit for closing the ends of tubular wrappings enclosing respective groups of cigarettes.